THE CHEMICAL-KINETICS OF HONO FORMATION RESULTING FROM HETEROGENEOUS INTERACTION OF NO2 WITH FLAME SOOT

Uptake experiments at ambient temperature of NO2 on ethylene, acetylen e and toluene soot resulted in significant amounts of MONO. The initia l uptake coefficient gamma(0) of NO2 on ethylene soot decreased from 0 .12 to 0.03 with increasing NO2 concentration in the range 8 x 10(10) to 1.4 x 10(13) molecule s(-1). The HONO yields relative to NO2 taken up were in the range 50 to 93% and were consistent with a mechanism in which either soot or hydrogen contained in it was the reducing agent. The branching ratio of the yield of HONO and NO was a function of the sampling spot at which the soot was collected within a diffusion flam e and ranged from 23 to 2.2 with increasing distance from the flame ba se and thus age. The total amount of HONO generated in one uptake expe riment was 1.2 x 10(16) molecules per mg of soot. Heating cycles bring back the ability of soot to generate MONO, but at diminishing yields.